landing: full pass — datapoints, copy button, binary downloads, carousel

- Update binary size: 5 MB → ~8 MB
- Update dependencies: 'one indirect dep' → '2 indirect (go-vector, net)'
- Add copy-to-clipboard buttons on all go install code blocks
- Add Binary downloads section with platform cards (linux amd64/arm64,
  darwin amd64/arm64) and download links
- Add 6-slide terminal carousel with console examples showing:
  file query, multi-turn session, sandbox mode, parallel sub-agents,
  MCP server mode, Web UI with token stats
- Carousel auto-advances every 8s, pauses on hover, manual nav buttons
- Add Demo section nav link
- Restore missing .cmd-list CSS class
- Platform tags (static binary, no root, etc.)

Author: jkyberneees